The present invention relates to ophthalmic lenses. In particular, the invention provides methods and compositions for producing lenses by casting.
The use of spectacle lenses for the correction of ametropia is well known. For example, multifocal lenses, such as progressive addition lenses, are used for the treatment of presbyopia. A number of methods are known for producing ophthalmic lenses. These methods include casting semi-finished lens blanks and subsequently polishing and grinding the blanks to form lenses, casting of whole lenses, and casting of a surface onto an optical preform to form a lens.
The casting of a surface onto an optical preform is advantageous in that it can reduce the number of molds required to produce a full prescriptive range of lenses. However, the known surface casting processes lack the efficiency necessary for use of the processes in the mass production of lenses. More specifically, the known processes require cure times of 30 minutes or more to achieve a cured resin layer free of optical distortions, defects, or voids. Additionally, known resins for use in surface casting processes cannot provide both a high refractive index on cure and a low viscosity at room temperature. Therefore, the invention provides methods and compositions for casting surfaces onto preforms to form lenses that attempt to overcome these disadvantages.
The present invention provides methods and compositions for producing ophthalmic lenses, including multifocal spectacle lenses such as progressive addition lenses, as well as lenses produced using the methods and compositions of the invention. The invention, provides a fast and reliable method for producing ophthalmic lenses.
In one embodiment, the invention provides a method for producing an ophthalmic lens comprising, consisting essentially of, and consisting of the steps of: a.) exposing to low intensity ultraviolet light a mold assembly and a surface-forming effective amount of a resin comprising, consisting essentially of, and consisting of reactive groups, the low intensity UV light exposure carried out under conditions suitable to convert at least about 50 percent or more of the resin""s reactive groups; and b.) exposing, subsequently, the resin to high intensity UV light under conditions suitable to substantially complete through curing of the resin. In another embodiment, the invention provides lenses produced by this method.
By xe2x80x9cophthalmic lensxe2x80x9d is meant a contact lens, intraocular lens, spectacle lens and the like. Preferably, the lens formed by the method of the invention is a spectacle lens, more preferably a multifocal, most preferably a progressive addition lens. By xe2x80x9cmold assemblyxe2x80x9d is meant one or more mold halves, an optical preform, or combinations thereof. By xe2x80x9coptical preformxe2x80x9d or xe2x80x9cpreformxe2x80x9d is meant a shaped, optically transparent article capable of refracting light, which article is suitable for use in producing a spectacle lens. By xe2x80x9cresinxe2x80x9d is meant at least one monofunctional monomer, one or more polyfunctional monomers, and one or more initiators. By xe2x80x9cconvertxe2x80x9d is meant that the reactive groups are incorporated into the polymer being formed.
In the first step of the method of the invention, a mold assembly is exposed to low intensity ultraviolet light. For purposes of the invention, low intensity UV light is UV light with an intensity of about 0.5 to about 50, preferably about 1 to about 5 mW/cm2. Suitable wavelengths for carrying out this step of the process are about 300 to about 450, preferably about 360 to about 400 nm. The low intensity exposure is carried out under conditions of wavelength and time suitable to convert at least about 50 percent or more of the resin""s reactive groups and, preferably, while maintaining the rate of polymerization as low as possible, which rate is a rate at which undesirable shrinkage induced defects are avoided. One ordinarily skilled in the art will recognize that this rate will depend on a number of factors including, without limitation, the resin used and the thickness of the resin layer. The maintenance of the low polymerization rate is achieved through the use of the low intensity UV light and, optionally, one or more of using a photoinitiator concentration of about 1 weight percent or less based on the total resin weight, incorporation of periods of non-exposure into the low intensity exposure cycle, and combinations thereof.
The time for the low intensity exposure will depend on the resin selected for casting onto the preform, the type and amount of initiator used, resin viscosity, the nature of the reactive groups, the thickness of the resin layer to be cast, and the intensity of the UV light. Generally, the total exposure time will be about 5 seconds to about 300 seconds, preferably about 60 seconds to about 120 seconds.
The low intensity exposure preferably is carried out in one step. However, some lens assemblies may require that the low intensity exposure be carried out in two or more steps using periods of non-exposure to the UV light of about 5 to about 60 seconds between each low intensity exposure. Preferably, periods of exposure of about 30 to about 60 seconds are alternated with non-exposure periods of about 5 to about 60 seconds.
Subsequent to the termination of the low intensity exposure, the mold assembly is exposed to high intensity UV light under conditions suitable to complete through cure of the resin. The intensity of the UV light for this step may be about 50 to about 2000, preferably 500 to about 1500 mW/cm2. The wavelength at which the exposure is carried out may be, and preferably is, the same as that used to carry out the low intensity exposure. The same factors determinative for low intensity exposure time are determinative for the high intensity exposure time. Generally, the exposure time will be about 3 seconds to about 60 seconds, preferably about 5 seconds to about 15 seconds. The high intensity exposure may, and preferably is, carried out as a single, continuous exposure. However, the high intensity exposure also may be carried out using alternating periods of UV exposure and non-exposure periods.
It is a discovery of the invention that the disclosed cure process using low and high intensity exposure permits production of a cast layer substantially free of distortions, defects and voids using a total UV exposure, both low and high intensity, time of about 150 or less seconds. Preferably the total exposure time is about 130 seconds or less.
The low and high intensity polymerization steps may be carried out at ambient temperature and atmospheric pressure. Preferably, the resin is hot-coated and the polymerization process is carried out at about the glass transition temperature, or Tg, of the cured resin or above. By xe2x80x9chot-coatedxe2x80x9d is meant that the resin is heated before it is cast to about its Tg. Heating may be accomplished by any convenient means including, without limitation, use of an oven, heat circulator, or combination thereof. Polymerization at the preferred temperature is also achieved by any convenient means including, without limitation, maintaining the cure chamber at the preferred temperature by use of forced air.
The low and high intensity UV exposures may be carried out in any fashion that permits the even distribution of the light through the mold assembly. A convenient and preferred mode is to expose the mold assembly to the UV light by placing the UV light source beneath the mold assembly. Sources of low intensity UV light include, without limitation, mercury and xenon arc lamps, fluorescent-type bulbs, or the like, and combinations thereof. High intensity UV light sources include, without limitation, mercury, xenon, and mercury-xenon arc lamps, FUSION(trademark) microwave-ignited lamps, or the like, and combinations thereof Suitable sources for the UV light used in the invention are commercially available.
The mold half or halves used may be made of any suitable material including, without limitation, glass or plastic. The optical preforms used in the mold assemblies may be made of any suitable materials including, without limitation, polycarbonates, such as bisphenol A polycarbonates, allyl diglycol carbonates, such as diethylene glycol bisallyl carbonate (CR-39(trademark)), allylic esters, such as triallyl cyanurate, triallyl phosphate and triallyl citrate, acrylic esters, acrylates, methacrylates, such as methyl- ethyl- and butyl methacrylates and acrylates, styrenics, polyesters, poly ether phosphine oxides, and the like and combinations thereof. The preform may be produced by any convenient means including, without limitation, injection molding, injection-compression molding, thermoforming, casting, or the like.
In practice of the method of the invention, the rein may contain any mono- or polyfunctional monomer suitable for use for casting a surface onto an optical preform and containing the requisite reactive groups. The reactive groups required to be contained in the monomers used in the invention are photopolymerizable groups including, without limitation, free-radical polymerizable, photoanionic polymerizable, photocationic polymerizable groups, and the like, and combinations thereof. Preferably, resins with free-radical polymerizable groups are used. Examples of such groups include, without limitation, substituted vinyl and allyl groups including, without limitation, acrylate, methacrylate, styryl, allylic esters, vinylic esters, allyl carbonates, allyl alkyl ethers, allyl aryl ethers and the like, and combinations thereof. As another alternative, the reactive groups may be photocationically reactive groups, such as an epoxide, aliphatic cyclic ether, vinyl alkyl and vinyl aryl ethers, styrenic groups, and the like and combinations thereof. As still another alternative, photoanionic reactive groups may be used including, without limitation, acrylate, methacrylate, epoxide, styryl, and the like, and combinations thereof.
Suitable mono- and polyfunctional monomers include, without limitation, hose disclosed in U.S. Pat. No. 5,470,892, incorporated in its entirety herein by reference. Additional suitable monomers include, without limitation, allyl and bis(allyl) carbonates, such as diethylene glycol bis(allyl) carbonate, bisphenol A diallyl carbonate, and the like, acrylic acid, multi-functional acrylates and methacrylates, such as ethylene glycol diacrylate, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, trimethylolpropane triacrylate, tetrahydrofurfuryl methacrylate, tetrahydrofurfuryl acrylate, hexanediolmethacrylate, methyl methacrylate, butyl methacrylate, propyl methacrylate, pentaerythritol tetraacrylate, urethane acrylates and methacrylates, styrene and styrene derivatives such as divinyl benzene, 4-vinyl anisole, various esters or maleic and itaconic acids, methacrylic and acrylic anhydrides and the like, and combinations thereof. Such monomers are commercially available or methods for their production are known.
It is another discovery of the invention that certain monomers are particularly useful in forming lenses with high refractive indices. By xe2x80x9chigh refractive indexxe2x80x9d is meant a refractive index on curing of about 1.54 or greater, preferably of about 1.56 or greater. The monomers useful in forming high refractive index resins are bisphenol A, diacrylates and dimethacrylates, ethoxylated bisphenol A diacrylates and dimethacrylates, acrylate and methacrylate esters of diglycidyl bisphenol A, epoxy acrylates and methacrylates, acrylates and methacrylates of tetrabromo bisphenol A, acrylates and methacrylates of bisphenol S, acrylate and methacrylate esters of diglycidyl tetrabromo bisphenol A, acrylate and methacrylate esters of diglycidyl tetrabromo bisphenol S, acrylate and methacrylate esters of tetrahydrofuran, and the like. The monomers may be used alone or in combination with one or more of the following: epoxy acrylates and methacrylates; ethoxylated phenoxy acrylates and methacrylates; isobornyl acrylates and methacrylates; divinyl benzene; benzyl acrylates and methacrylates; polyethylene glycol diacrylates and dimethacrylates; N-vinyl carbazole, and the like.
In formulations using ethoxylated bisphenol A, the weight percentages of the ethoxylated bisphenol A component may be about 1 to about 99, preferably about 4 to about 80, more preferably about 20 to about 75 weight percent of the total weight of the resin composition. The ethoxylated bisphenol A component may be a mixture of at least two ethoxylated bisphenol A components, the first component of about 2 to about 4 and the second component of about 9 to about 11 mole, preferably about 3 and about 10 mole, respectively. The weight percentages for the first component may be about 30 to about 60 and the second about 0 to about 30 weight percent, preferably about 40 to about 50 and about 20 to about 30 weight percent, respectively, based on the total weight of the resin used. A preferred composition for use as the casting resin is about 30 to about 80 weight percent of ethoxylated bisphenol A diacrylate (preferably about 40 to about 50 weight percent of about 3 mole and about 20 to about 30 weight percent of about 10 mole) and about 24 to about 50 weight percent of 2-phenoxyethyl acrylate. A particularly preferred composition is about 75 weight percent of ethoxylated bisphenol A (about 50 weight percent of about 3 mole and about 25 weight percent of about 20 mole) and about 24 weight percent 2-phenoxyethyl acrylate.
In a preferred embodiment, the invention provides a method for producing a lens comprising, consisting essentially of, and consisting of the steps of: a.) exposing a mold assembly and a resin comprising, consisting essentially of, and consisting of about 30 to about 80 weight percent of ethoxylated bisphenol A diacrylate and about 24 to about 50 weight percent of 2-phenoxyethyl acrylate to low intensity UV light under conditions suitable to convert at least about 50 percent or more of the resin""s reactive groups; and b.) exposing, subsequently, the resin to high intensity UV light under conditions suitable to complete through curing of the resin.
The viscosity of the resin may be about 5 to about 500, preferably less than about 300, more preferably about 5 to about 300, most preferably about 5 to about 100 centipoise measured at 25xc2x0 C. with a Brookfield viscometer. It is another discovery of the invention that it is possible to obtain a suitable resin with both a high refractive index and a viscosity of less than about 300 cp. One ordinarily skilled in the art will recognize that the weight percentages of the mono- and polyfunctional monomers must be controlled so as to achieve the desired viscosity.
Additionally, the glass transition temperature, or Tg, of the cured resin used preferably is greater than about 45xc2x0 C. One ordinarily skilled in the art will recognize that the Tg of the cured resin should not differ significantly, preferably not by more than about 1 to about 10xc2x0 C. from that of the material used to form the optical preform. Preferably, the Tg of the cured resin and optical preform material are substantially the same. Further, one ordinarily skilled in the art will recognize that the desired cured resin Tg is achievable by selection of monomers and their concentrations.
The monomers selected may have about 0.04 to about 1.17, preferably about 0.15 to about 1.2 equivalents of reactive groups per 100 g resin. Preferably, the monomers used contain about 0.4 to about 0.6 reactive group equivalents per 100 g resin. The amount of resin cast-will be an amount effective to form a surface, which amount will depend on the resin selected, the parameters of the surface desired to be formed, and the size and shape of the surface on which the resin will be cast. Typically, the amount of resin used will be about 2 to about 20 g.
Photoinitiators useful in the invention are those capable of initiating polymerization of the cast resin in the UV absorption spectrum selected. Suitable initiators include, without limitation, free-radical generating photoinitiators, photocationic initiators, photobase initiators, and mixtures thereof. Suitable free-radical generating initiators include, without limitation, methyl benzoyl formate, aromatic ketones including, without limitation, 2-hydroxy-2-methyl-1-phenyl-5 propan-1-one, 1-hydroxycyclohexylphenylketone, 2,2-di-secbutoxyacetophenone, 2,2-diethoxyacetophenone, 2,2-diethoxy-2-phenyl-acetophenone, 2,2-dimethoxy-2-phenyl-acetophenone, benzoin methyl ether, benzoin isobutyl ether, benzoin, benzil, benzil dimethyl ketal, benzyl disulfide, 2,2-dihydroxybenzophenone, benzylideneacteophenone, benozphenone, and acetophenone, 2,4,6-trimethylbenzoyldiphenoylphosphine oxide, and the like, and combinations thereof. Suitable free-radical generating initiators are commercially available or methods for their production known.
Exemplary photocationic initiators include, without limitation, triarylsulfonium salts, such as triphenylsulfonium hexafluoroantimonate and triphenylsulfonium hexafluorophospate, diarylodonium salts such as di-(4-dodecylphenyl)iodonium hexafluorophosphate, aryl diazonium salts, and the like and combinations thereof. Suitable photocationic initiators are commercially available or methods for their production are known.
Exemplary photobase initiators include, without limitation, ortho-nitrobenzyl carbamates such as 4,5-dimethoxy-2-nitrobenzyl carbamate, N-{[4,5-dimethoxy-2-nitrobenzyl)oxy]-carbonyl-2,6-dimethylpiperidine}, 3,5,-dimethoxy-xcex1, xcex1-dimethylbenzyl carbamates, benzoin carbamates such as 3,3xe2x80x2,5,5xe2x80x2-dimethoxy benzoin carbamate, o-acyloximes, ammonium salts of xcex1-ketocarboxylic acids, such as dimethyl benzyl ammonium phenylglyoxylate, cobalt (III) alkylamine complexes such as trans-[Co(pyridine)4Cl2]Cl, and the like, and combinations thereof. Methods for their production are disclosed in: 1.) Cameron, J. F. and J. M. Frechet, 113 J. Am. Chem. Soc., 4303-4313 (1991); 2.) Cameron, J. F. and J. M. Frechet, 55 J. Org. Chem., 5919-5922 (1990); and 3.) Weit, S. K., C. Kutal, and R. D. Allen, 4 Chem. Mater., 453-457 (1992).
The amount of initiator used will depend on the type of initiator selected as well as the resin formulation used. Typically, the amount of initiator will be an amount effective to initiate polymerization, about 0.1 to about 5 weight percent based on the weight of the resin formulation, preferably about 0.1 to about 1 weight percent. In addition to a suitable initiator, the resin of the invention may include any desired additive, including without limitation, crosslinkers, viscosity control agents, and the like, and combinations thereof.
One ordinarily skilled in the art will recognize that the curing of the resin may be carried out by curing methods in addition to the preferred UV light cure of the invention. For example, thermal, microwave, and infra-red radiation curing may be used alone or in combination with UV curing.
Casting of the resin onto the preform to form a surface or surfaces may be accomplished by any known method. Suitable methods, for casting one or more surfaces of a preform are disclosed in U.S. Pat. Nos. 5,147,585, 5,178,800, 5,219,497, 5,316,702, 5,358,672, 5,480,600, 5,512,371, 5,531,940, 5,702,819, 5,793,465, 5,859,685, 5,861,934, and 5,907,386 incorporated herein in their entireties by reference.
In general, the resin is dispensed into the mold assembly using any convenient means, such as by the use of a displacement pump. Preferably, the mold assembly is formed of one mold half and an optical preform, the preform acting as the second mold half. The resin may be dispensed so as to form, when cured, one or both of a convex and concave surface, preferably a convex surface, on the preform. Preferably, the mold half is positioned, the resin is dispensed onto a surface of the mold half and the preform is then contacted with the resin by placing the preform on the resin. Once the mold half and preform are positioned as desired, additional resin may be dispensed into the mold assembly to ensure the elimination of air bubbles and voids.
Preferably, the mold half or halves used are of a greater diameter than that of the optical preform. This permits containment of the resin without the use of a gasket, sealing ring, or similar equipment. In those cases in which the curve radius of the preform surface in contact with the resin and mold half is less than that of the mold half, the use of a spacing means may be necessary. By xe2x80x9cspacing meansxe2x80x9d is meant any equipment suitable for use in maintaining the desired distance between the mold half surface and the optical preform surface in contact with the resin. Exemplary equipment for use as spacing means include, without limitation, tapes, gaskets, O-rings, and the like.
Once the curing of the resin is completed, the mold assembly is disassembled to separate the lens from the mold half or halves. Any convenient means may be used for separating the lens from the mold assembly including, without limitation, mechanical separation, thermal separation, and the like, and combinations thereof. It is a further discovery of the invention that disassembly may be achieved by using a water bath and ultrasound. More specifically, separation of the lens, including the cast surface, from the mold is achieved by using ultrasound in the range of about 25 to about 150, preferably 40 to about 50 Khertz induced into a container filled or partially filled with water. The water temperature used will depend on the temperature of the mold assembly; the higher the mold assembly temperature, the higher the water temperature used. Typically, the water temperature will be about room temperature to about xe2x88x925xc2x0 C.
Optionally, and preferably, following disassembly of the mold assembly, the lens is heated for a time and at a temperature suitable to relieve stresses resulting from the polymerization process. Heating may be carried out by any convenient method including, without limitation, using thermal, infrared, or microwave energy or combinations thereof. Preferably, the lens is heated using thermal energy for about 1 to about 30, preferably about 5 to about 15 mins at a temperature of about 50 to about 125, preferably about 80 to about 110xc2x0 C.
One ordinarily skilled in the art will recognize that any type of lens including, without limitation, singlevision, flat-top, multifocal including, without limitation, bifocal, trifocal, progressive, or the like, may be produced using the method of the invention. However, the invention may find greatest utility in the production of progressive addition lenses using surface casting. In embodiments in which the desired final lens is a bifocal, the preform, the added layer, or both must provide near vision power in addition to distance power. For embodiments in which the final lens is a progressive addition lens, the preform, cast layer, or both must provide near vision power, distance power and a zone of transition power between the distance and near vision power zones. For example, a surface of the preform or the cast layer may form a progressive addition surface thus providing a progressive addition lens as the final lens. By xe2x80x9cprogressive addition surfacexe2x80x9d is meant a continuous, aspheric surface having distance and near vision zones and a zone of transition power, or zone of increasing dioptric power, connecting the distance and near vision zones.